/* Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved. */
package com.nulldev.util.internal.backport.optionals;

import java.util.NoSuchElementException;
import java.util.function.LongConsumer;
import java.util.function.LongSupplier;
import java.util.function.Supplier;

/**
 * A container object which may or may not contain a {@code long} value. If a
 * value is present, {@code isPresent()} will return {@code true} and
 * {@code getAsLong()} will return the value.
 *
 * <p>
 * Additional methods that depend on the presence or absence of a contained
 * value are provided, such as {@link #orElse(long) orElse()} (return a default
 * value if value not present) and
 * {@link #ifPresent(java.util.function.LongConsumer) ifPresent()} (execute a
 * block of code if the value is present).
 *
 * <p>
 * This is a <a href="../lang/doc-files/ValueBased.html">value-based</a> class;
 * use of identity-sensitive operations (including reference equality
 * ({@code ==}), identity hash code, or synchronization) on instances of
 * {@code OptionalLong} may have unpredictable results and should be avoided.
 *
 * @since 1.8
 */
public final class OptionalLong {
	/**
	 * Common instance for {@code empty()}.
	 */
	private static final OptionalLong EMPTY = new OptionalLong();

	/**
	 * If true then the value is present, otherwise indicates no value is present
	 */
	private final boolean isPresent;
	private final long value;

	/**
	 * Construct an empty instance.
	 *
	 * @implNote generally only one empty instance, {@link OptionalLong#EMPTY},
	 *           should exist per VM.
	 */
	private OptionalLong() {
		this.isPresent = false;
		this.value = 0;
	}

	/**
	 * Returns an empty {@code OptionalLong} instance. No value is present for this
	 * OptionalLong.
	 *
	 * @apiNote Though it may be tempting to do so, avoid testing if an object is
	 *          empty by comparing with {@code ==} against instances returned by
	 *          {@code Option.empty()}. There is no guarantee that it is a
	 *          singleton. Instead, use {@link #isPresent()}.
	 *
	 * @return an empty {@code OptionalLong}.
	 */
	public static OptionalLong empty() {
		return EMPTY;
	}

	/**
	 * Construct an instance with the value present.
	 *
	 * @param value the long value to be present
	 */
	private OptionalLong(long value) {
		this.isPresent = true;
		this.value = value;
	}

	/**
	 * Return an {@code OptionalLong} with the specified value present.
	 *
	 * @param value the value to be present
	 * @return an {@code OptionalLong} with the value present
	 */
	public static OptionalLong of(long value) {
		return new OptionalLong(value);
	}

	/**
	 * If a value is present in this {@code OptionalLong}, returns the value,
	 * otherwise throws {@code NoSuchElementException}.
	 *
	 * @return the value held by this {@code OptionalLong}
	 * @throws NoSuchElementException if there is no value present
	 *
	 * @see OptionalLong#isPresent()
	 */
	public long getAsLong() {
		if (!isPresent) {
			throw new NoSuchElementException("No value present");
		}
		return value;
	}

	/**
	 * Return {@code true} if there is a value present, otherwise {@code false}.
	 *
	 * @return {@code true} if there is a value present, otherwise {@code false}
	 */
	public boolean isPresent() {
		return isPresent;
	}

	/**
	 * Have the specified consumer accept the value if a value is present, otherwise
	 * do nothing.
	 *
	 * @param consumer block to be executed if a value is present
	 * @throws NullPointerException if value is present and {@code consumer} is null
	 */
	public void ifPresent(LongConsumer consumer) {
		if (isPresent)
			consumer.accept(value);
	}

	/**
	 * Return the value if present, otherwise return {@code other}.
	 *
	 * @param other the value to be returned if there is no value present
	 * @return the value, if present, otherwise {@code other}
	 */
	public long orElse(long other) {
		return isPresent ? value : other;
	}

	/**
	 * Return the value if present, otherwise invoke {@code other} and return the
	 * result of that invocation.
	 *
	 * @param other a {@code LongSupplier} whose result is returned if no value is
	 *              present
	 * @return the value if present otherwise the result of
	 *         {@code other.getAsLong()}
	 * @throws NullPointerException if value is not present and {@code other} is
	 *                              null
	 */
	public long orElseGet(LongSupplier other) {
		return isPresent ? value : other.getAsLong();
	}

	/**
	 * Return the contained value, if present, otherwise throw an exception to be
	 * created by the provided supplier.
	 *
	 * @apiNote A method reference to the exception constructor with an empty
	 *          argument list can be used as the supplier. For example,
	 *          {@code IllegalStateException::new}
	 *
	 * @param <X>               Type of the exception to be thrown
	 * @param exceptionSupplier The supplier which will return the exception to be
	 *                          thrown
	 * @return the present value
	 * @throws X                    if there is no value present
	 * @throws NullPointerException if no value is present and
	 *                              {@code exceptionSupplier} is null
	 */
	public <X extends Throwable> long orElseThrow(Supplier<X> exceptionSupplier) throws X {
		if (isPresent) {
			return value;
		} else {
			throw exceptionSupplier.get();
		}
	}

	/**
	 * Indicates whether some other object is "equal to" this OptionalLong. The
	 * other object is considered equal if:
	 * <ul>
	 * <li>it is also an {@code OptionalLong} and;
	 * <li>both instances have no value present or;
	 * <li>the present values are "equal to" each other via {@code ==}.
	 * </ul>
	 *
	 * @param obj an object to be tested for equality
	 * @return {code true} if the other object is "equal to" this object otherwise
	 *         {@code false}
	 */
	@Override
	public boolean equals(Object obj) {
		if (this == obj) {
			return true;
		}

		if (!(obj instanceof OptionalLong)) {
			return false;
		}

		OptionalLong other = (OptionalLong) obj;
		return (isPresent && other.isPresent) ? value == other.value : isPresent == other.isPresent;
	}

	/**
	 * Returns the hash code value of the present value, if any, or 0 (zero) if no
	 * value is present.
	 *
	 * @return hash code value of the present value or 0 if no value is present
	 */
	@Override
	public int hashCode() {
		return isPresent ? Long.hashCode(value) : 0;
	}

	/**
	 * {@inheritDoc}
	 *
	 * Returns a non-empty string representation of this object suitable for
	 * debugging. The exact presentation format is unspecified and may vary between
	 * implementations and versions.
	 *
	 * @implSpec If a value is present the result must include its string
	 *           representation in the result. Empty and present instances must be
	 *           unambiguously differentiable.
	 *
	 * @return the string representation of this instance
	 */
	@Override
	public String toString() {
		return isPresent ? String.format("OptionalLong[%s]", value) : "OptionalLong.empty";
	}
}
